The present invention is generally directed to toner compositions, and more specifically to encapsulated colored heat fusible toner compositions. In one embodiment, the present invention is related to low melting encapsulated colored toner compositions comprised of a core with a polymeric shell thereover preferably prepared by interfacial polymerization. Another specific embodiment of the present invention relates to encapsulated colored toner compositions comprised of a core containing a preformed polymer and/or monomers, a free radical initiator which initiates the free radical polymerization of the core monomers when heated, pigment dye particles, or mixtures thereof, and wherein the core is dispersed into an emulsifier solution, and subsequently encapsulated by a polymeric shell followed by core polymerization at elevated temperatures via free radical polymerization with the emulsifier or surfactant being comprised of organic methyl cellulose, hydroxylatedmethyl cellulose components, such as Tylose available from Fluka Inc. of Canada, or Methocel available from Dow Chemical, or mixtures thereof. In another embodiment of the present invention there may be selected as the emulsifier or surfactant the aforementioned emulsifiers with other emulsifiers such as poly(vinyl alcohol). Several advantages are associated with the encapsulated toners of the present invention including their desirable heat fusibility, triboelectric passivation of the components, especially the pigment components present in the core thereby avoiding or minimizing the electrical, especially the triboelectrical, degradation properties of the resulting toner caused by the pigment particles; narrow size distribution of the particles (GSD) of, for example, from 1.5 to about 1.8; stable shell characteristics, dissolvable blocking temperatures, for example in an embodiment of the present invention blocking temperatures for the heat fusible toners, especially with polyurea shells, of greater than 80.degree. C.; avoidance or minimization of particle agglomeration and coalescence, especially at elevated core polymerization temperatures; excellent melt flow properties, for example from about 10.degree. to about 20.degree. C. lower than a toner comprised of styrene n-butylmethacrylate, 88 weight percent, 10 weight percent of carbon black, and 2 weight percent of cetyl pyridinium chloride as a charge enhancing additive, and the like. In another embodiment of the present invention, there can be included in the encapsulated toner compositions optional surfactants such as anionic, cationic as well as ambithillic and nonionic materials. Particularly useful as surfactants are fluorinated hydrocarbons such as fluoride FC-170C. available from 3M; Zonyl FSA available from E.I. DuPont, and Zonyl FSN available from E.I. DuPont, which surfactants may, in an embodiment of the present invention, be utilized in combination with surfactants such as polyvinyl alcohol.
Toners suitable for use in electrophotographic apparatuses, including printers, may include therein a wide variety of colors, such as black, red, green, blue, brown, yellow, purple, silver and gold. When it is desired to highlight certain features of a document, one or more colored toners are typically used in conjunction with a black toner to provide an image in two or more colors. Full color images can also be generated by developing images with cyan, magenta, yellow and black toners. Generally, it is advantageous for such toners to exhibit low melting temperatures to enable low energy fusing of the developed images to substrates at lower temperatures and lower pressures of 400 psi versus 4,000 psi for many prior art cold pressure fixable applications. It is also often advantageous for such toners to possess mean particle diameters of from about 5 microns to about 35 microns and preferably from about 5 microns to about 15 microns to enable images of high resolution, low image noise and high color fidelity. Further, it is generally desirable for these small diameter toners to possess very narrow size distributions, preferably with a GSD (Geometric Standard Deviation) of 1.3 or less, to avoid difficulties in the electrophotographic development and transfer associated with oversize toner particles and extremely fine toner particles. These and other advantages can be achieved with the encapsulated toners and processes of the present invention in embodiments thereof. More specifically, an advantage associated with the toners of the present invention in an embodiment thereof is the enablement of preparing both heat fusible low Tg (&lt;130.degree. C.) shell and low Tg (&lt;55.degree. C.) core compositions comprised of a styrene/stearyl methacylate core with pigment and emulsifier and meta-tetramethylxylene diisocyanate (m-TMXDI) and 1,3-cyclohexanebis(methylamine) CHBMA shell which provides melt flow properties 10.degree. to 20.degree. C. lower than a toner comprised of resin particles, such as stryen/n-butyl methacrylate copolymer, carbon black, and the charge enhancing additive cetyl pyridinium chloride. Also, with a shell of metatetramethylxylene diisocyanate (m-TMXDI) and 2-methylpentamethylenediamine (Dytek A) and with the aforementioned core components there are enabled improvements in heat fusibility of the particles by permitting softening and/or melting of the shell during the fusing process. In an embodiment of the present invention, the incorporation into the toner core of Tylose 93800, a hydroxyethylmethyl cellulose or other emulsifier as illustrated herein is advantageous since, for example, it enables a narrower GSD value for the particles, which is determined at the dispersion step, of from 1.6 to 1.35 especially for colored heat fusible toners, and also the Tylose is an excellent dispersing agent at elevated temperatures such as 85.degree. C. during the free radical polymerization step, thus an additional dispersant component such as Daxad is not required to prevent particle agglomeration and coalescence even with low Tg shells. Another advantage of using Tylose as the emulsifier is that when incorporated into the shell, it does not usually adversely affect the melt flow properties of the toner particles and thus does not substantially increase the fusing temperature of the toner as is the situation with a poly(vinylalcohol) emulsifier. Improved toner compositions have also been prepared by incorporating polyether backbone prepolymers and the like into the heat fusible shell to improve shell flexibility and overall fusibility of the toner. The blocking temperatures of the particles prepared with both a heat fusible shell and core wherein, for example, Tylose is present as an emulsifier is equal to or greater than 80.degree. C. in an embodiment of the present invention. With the incorporation of Tylose or other similar emulsifier as illustrated herein, pigment passivation is accomplished. Also, with the emulsifiers illustrated herein, especially Tylose, the toner particle size and distribution can be improved resulting in a narrow tribo range when charged, for example, against different carriers.
The toner compositions of the present invention can be selected for a variety of known imaging and printing processes including electrophotographic processes. Specifically, the toner compositions of the present invention can be selected for xerographic imaging and printing processes including color processes, such as two component development systems and single component development systems, including both magnetic and nonmagnetic; and ionographic processes wherein dielectric receivers such as silicon carbide are utilized, reference U.S. Pat. No. 4,885,220, the disclosure of which is totally incorporated herein by reference.
In a patentability search report, there were recited as prior art the following U.S. Pat. Nos. 4,830,144 directed to encapsulated pressure fixable toners with an electroconductive powder coating, reference, the Abstract of the Disclosure, and the disclosure beginning in column 3, around line 48. Examples of shell components are illustrated in column 4, beginning at around line 33, and note specifically the disclosure in column 4, beginning at line 47, wherein shells are produced by the polycondensation reaction between polyisocyanates and one or more of the counterpart compounds such as polyol, polythio, polyamine, water, and perpazine can be selected; the preparation of the encapsulated toner of this patent is illustrated in column 7, beginning at line 6; examples of colorants included in the core, which colorants may comprise dyes, pigments, and the like, are illustrated beginning in column 8; surface active agents selected for the encapsulated toner of the '144 patent are illustrated in column 11, while examples of the electroconductive material include components such as antimony, halogen, and the like, reference Claim 1, for example; U.S. Pat. No. 4,721,651 directed to microcapsules of the type selected for pressure sensitive carbonless copy papers with walls formed of an aliphatic diisocyanate and a diamine and containing, for example, a solvent mixture with a dye precursor dissolved therein, note for example the disclosure beginning in column 2, the working Examples, and Claim 1; a similar teaching is present in U.S. Pat. No. 4,622,267; U.S. Pat. No. 4,738,898 directed to microencapsulation by interfacial polyaddition of, for example, an aliphatic diisocyanate and an isocyanurate triamer, and wherein the aforementioned components can be interfacially reacted with a polyamine; the selection of carboxy methylcellulose, sodium salt, is illustrated in the working Examples, reference working Example 1, column 5, beginning at line 26; further, note the disclosure in column 3, beginning at line 46, wherein it is indicated that it is envisioned, for example, to encapsulate plant protection agents such as herbicides, fungicides, or insecticides, which makes then less hazardous to handle, and it is also intended to encapsulate the pharmaceutical products, food products, flavors, perfumes, colorants, paints, or catalysts, reference the disclosure in column 3, beginning at line 46; U.S. Pat. No. 4,766,051, the disclosure of which is totally incorporated herein by reference, directed to colored encapsulated toner compositions, more specifically, cold pressure fixable colored toner compositions comprised of a core containing a polymer in which is dispersed pigment particles selected from the group consisting of cyan, magenta, red, yellow pigments, and mixtures thereof, and magnetites encapsulated within a polymeric shell formulated by an interfacial polymerization, note specifically, for example, the disclosure in column 3, beginning at line 35, and continuing on to column 15, and note that polyvinyl alcohol may be selected, and more specifically, for example, the organic phase can be dispersed by a polytron in an aqueous phase containing polyvinyl alcohol to obtain toner particles, see column 6, beginning at line 28, and note specifically the working Examples, especially working Example 11; and U.S. Pat. No. 4,193,889 directed to microencapsulation with modified polyisocyanates, and more specifically to microcapsules and a process therof, the walls of which consist of polycondensates of a film forming aliphatic polyisocyanate containing at least one biurett group or polyaddition products thereof with a chain extending agent, reference the Abstract of the Disclosure; and note the disclosure in columns 2, 3 and 4.
In a copending application directed to encapsulated toner, there were mentioned in a patentability search report the following U.S. Pat. Nos. 4,727,101, the disclosure of which is totally incorporated herein by reference, which illustrates a free radical polymerization of a toner shell at elevated temperatures and more specifically is directed to the preparation of encapsulated toner compositions, which comprises mixing in the absence of a solvent a core monomer, initiator, pigment particles, a first shell monomer, stabilizer, and water, and thereafter adding a second shell monomer to enable interfacial polymerization interaction, and subsequently affecting the free radical polymerization of the core monomer, reference the Abstract of the Disclosure for example; U.S. Pat. No. 4,777,104 the disclosure of which is totally incorporated herein by reference, which relates to processes for the formation of electrophotographic toners of certain desired sizes by radical polymerization, reference for example column 3, lines 26 to 41, and also note the disclosure in column 6 with respect to colorants, beginning at line 29; U.S. Pat. No. 4,524,199, the disclosure of which is totally incorporated herein by reference, which relates to stable polymeric dispersions, which dispersion comprises, for example, a polar dispersion medium having dispersed therein particles comprising a thermoplastic resin core having irreversibly anchored thereto a nonionic amphipathic steric stabilizer comprising a graft copolymer, reference for example column 2, beginning at line 45, and note column 4, beginning at line 57, and continuing on to column 5; U.S. Pat. No. 4,533,617 the disclosure of which is totally incorporated herein by reference, directed to heat fixable developers with a capsule structure containing a binder resin of a certain glass transition temperature and a colorant coated with a vinyl type polymer, reference for example the Abstract of the Disclosure, and note columns 4 through 10; U.S. Pat. No. 4,725,522 directed to processes for cold pressure fixable encapsulated toner compositions, particularly processes thereof wherein a water phase containing a stabilizing material is selected and hydrolysis is accomplished by heating and there is utilized interfacial polymerization to form the shell, reference for example the Abstract of the Disclosure, and also note columns 4 to 8, the disclosure of the aforementioned patent being totally incorporated herein by reference; U.S. Pat. No. 3,876,610 relating to the preparation of electrostatic toner materials with a size between 1 to 10 microns and containing a polymeric shell comprising a copolymer with a glass transition temperature of at least 40.degree. C., see the Abstract of the Disclosure for example, the disclosure of the aforementioned patent being totally incorporated herein by reference; and U.S. Pat. No. 4,762,752 which discloses additional compounds suitable as dispersing agents, reference the Abstract of the Disclosure, for example the disclosure of the aforementioned patent being totally incorporated herein by reference.
Additionally, there is illustrated in U.S. Pat. No. 4,565,764 a pressure fixable microcapsule toner having a colored core material coated successively with a first resin wall and a second resin wall. The first resin wall has affinity to both the core material and the second resin wall. This patent teaches that the first resin wall may be of a material that becomes charged to a polarity opposite to that of the second resin wall and the core material.
Also, U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, illustrates a pressure fixable encapsulated electrostatographic toner material. The core comprises a colorant, a polymer, a solvent capable of dissolving the polymer or causing the polymer to swell, and an organic liquid incapable of dissolving the polymer or causing the polymer to swell, while the shell may consist of a polyamide resin. Preparation of the toner material is completed by interfacial polymerization.
Another patent, U.S. Pat. No. 4,708,924, the disclosure of which is totally incorporated herein by reference, describes a pressure fixable microcapsule type toner composed of a core material and an outer wall covering over the core material. The core material contains at least a combination of a substance having a glass transition point within the range of -90.degree. C. to 5.degree. C. with a substance having a softening point within the range of 25.degree. C. to 180.degree. C. This toner composition may comprise substances, such as polystyrene and poly(n-butylmethacrylate), and their copolymers.
Further, U.S. Pat. No. 4,254,201, the disclosure of which is totally incorporated herein by reference, illustrates a pressure sensitive adhesive toner consisting essentially of porous aggregates. Each aggregate consists essentially of a cluster of a multiplicity of individual granules of pressure sensitive adhesive substance, each granule being encapsulated by a coating film of a film-forming material. Particles of an inorganic or organic pigment and/or a magnetic substance are contained within the aggregate in the interstices between the granules and deposited on the surface of the encapsulated granules. The adhesive substance is selected from a copolymer of at least one monomer and as many as three other monomers.
In addition, U.S. Pat. No. 4,702,988, the disclosure of which is totally incorporated herein by reference, illustrates a process for the preparation of encapsulated toner. A monomer composition and a colorant are dispersed in a liquid dispersion medium in the presence of a solid fine powdery dispersion stabilizer. The liquid is pressurized and then ejected into a low pressure section to form particles of monomer composition. These particles are then subjected to suspension polymerization to produce toner particles.
In U.S. Pat. No. 4,727,011 there is disclosed a process for preparing encapsulated toner compositions, which comprises mixing, in the absence of a solvent, a core monomer, an initiator, pigment particles, a first shell monomer, stabilizer, and water; thereafter adding a second shell monomer, thereby enabling an interfacial polymerization reaction between the first and second shell monomers; and subsequently effecting a free radical polymerization of the core monomer. The disclosure of this patent is totally incorporated herein by reference.
Also, U.S. Pat. No. 4,855,209, the disclosure of which is totally incorporated herein by reference, discloses an encapsulated toner composition with a melting temperature of from about 65.degree. C. to about 140.degree. C. which comprises a core containing a polymer selected from the group consisting of polyethylene succinate, polyhalogenated olefins, poly(.alpha.-alkystyrenes), rosin modified maleic resins, aliphatic hydrocarbon resins, poly(.epsilon.-caprolactones), and mixtures thereof; and pigment particles, where the core is encapsulated in a shell prepared by interfacial polymerization reactions. The disclosure of this copending application is totally incorporated herein by reference containing a stabilizing material, hydrolyzing by heating the resulting mixture, subsequently effecting an interfacial polymerization of the mixture, and thereafter optionally washing the resulting toner composition.
There are disclosed in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Copending application U.S. Ser. No. 043,265 (now abandoned) the disclosure of which is totally incorporated herein by reference, discloses an encapsulated composition suitable for use as an electrophotographic toner, which comprises a core encapsulated within a thermotropic liquid crystalline polymeric shell. On page 8 of this application, the specification indicates that the disclosed developer compositions can be charged to preselected values irrespective of the pigment selected for the core.
Further, U.S. Pat. No. 4,851,318 discloses an improved process for preparing encapsulated toner compositions which comprises mixing core monomers, an initiator, pigment particles, and oil soluble shell monomers, homogenizing the mixture into an aqueous surfactant solution to result in an oil-in-water suspension enabling an interfacial polymerization reaction between the oil soluble and the water soluble shell monomers, subsequently adding a low molecular weight polyethylene oxide surfactant protective colloid, and thereafter effecting free radical polymerization of the core monomers by heating. The disclosure of this U.S. Pat. No. 4,851,318 is totally incorporated herein by reference.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process.
There is illustrated in a U.S. Pat. No. 4,937,167, the disclosure of which is totally incorporated herein by reference, a process for controlling the electrical characteristics of colored toner particles. The process comprises preparing a first core material comprising first pigment particles, core monomers, a free radical initiator, and optional polymer components, said second pigment particles being of a different color from that of the first pigment particles; encapsulating separately the first core material and the second core material within polymeric shells by means of interfacial polymerization reactions between at least two shell monomers, of which at least one is soluble in aqueous media and at least one of which is soluble in organic media, wherein the polymeric shell encapsulating the first core material is of substantially the same composition as the polymeric shell encapsulating the second core material; and subsequently polymerizing the first and second core monomers via free radical polymerization thereby producing two encapsulated heat fusible toner compositions of different colors with similar triboelectric charging characteristics.
There is also illustrated in U.S. Pat. No. 5,035,970, the disclosure of which is totally incorporated herein by reference, an encapsulated toner composition comprised of a core comprised of pigments or dyes, and a polymer; and wherein the core is encapsulated in a polyester shell with functional groups thereon, and derived from diacid halide polyesters.
U.S. Pat. No. 5,037,716, the disclosure of which is totally incorporated herein by reference, illustrates encapsulated toners with a Daxad dispersant. To stabilize heat fusible particles at elevated temperatures, the addition of a Daxad dispersant is required to prevent particle agglomeration and coalescence. The encapsulated toner composition comprises a core comprised of a preformer polymer and/or monomer or monomers, a free radical initiator, pigment or dye particles where the core is dispersed in an emulsifier solution, and subsequently encapsulated in a polymeric shell and wherein the toner is stabilized by Daxad dispersants during core polymerization, where the dispersant is a naphthalene sulfonate formaldehyde condensate material. In this patent application, the system emulsifier was not able to lower the GSD below 1.5 without classification. The incorporation of Daxad can be added after the particle generation step, thus Daxad has no effect on narrowing the GSD down to the desired value of 1.3.
Free radical polymerization is well known art, and can be generalized as bulk, solution, emulsion or suspension polymerization. These polymerizations are commonly selected for the preparation of certain polymers. The kinetics and mechanisms for free radical polymerization of monomer(s) is also well known. In these processes, the control of polymer properties such as molecular weight and molecular weight dispersity can be effected by initiator, species concentrations, temperatures, and temperature profiles. Similarly, conversion of monomer is effected by the above variables.
There is a need for encapsulated toner compositions with many of the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein particle agglomeration is eliminated or minimized. Another need resides in obtaining improved particle stabilization during free radical polymerization of heat fusible color toners suitable for use in electrophotographic copiers and printers, and wherein dispersants are avoided. A need also exists for the stabilization of colored toners which exhibit low melting behavior, including a low melting core Tg&lt;55.degree. C., and a low melting polymeric shell Tg&lt;130.degree. C. without particle agglomeration or coalescence during free radical polymerization thereby enabling lower fusing temperatures, and wherein organic methyl cellulose or hydroxylatemethyl cellulose emulsifiers are selected. A further need exists for dry toners with an average mean diameter of from about 5 microns to about 15 microns and a narrow geometric size distribution of less than 1.5, and preferably 1.3 to about 1.4 without the need for micronization or classification. There is a further need for colored toner particles with clean, dirt free surfaces which aid in narrowing the size distribution (reduction of fines of less than 1 micron in an embodiment) and assist to narrow the triboelectric charging distribution of the developer. Additionally, there is a need for toners and processes of preparation thereof for decreasing and/or eliminating the generation of fine particles. Also, there is a need for encapsulated colored toners wherein a minimum amount of surfactant or emulsifier is selected to generate toner size particles. There is a further need for encapsulated colored toners for an improved process that will eliminate the grafting or incorporation of poly(vinylalcohol) into the shell at elevated temperatures. Also, there is a need for encapsulated colored toners wherein a higher loading of the organic phase into the aqueous phase can be accomplished. Further, there is a need for encapsulated toners wherein images with excellent resolution and no background development are obtained in an embodiment of the present invention. Additionally, there is a need for encapsulated toners, including colored toners wherein an emulsifier when incorporated into the shell does not substantially effect the melt flow properties and the fusing properties of the toner. There is a further need for encapsulated colored toners that enable shell flexibility and fusibility through the addition of polyether backbone prepolymers. Also, there is a need for the reduction of the tribo range for a series of differently pigmented toner samples to enable pigment passivation when charged against numerous carriers in an embodiment of the present invention.